In the prior art, the filtering net primarily filters dusts, particles or hairs in the air as an air filtering device of an air conditioner. The filtering net is an important element. The current used filtering net can be classified as a high density filtering net and a lower density filtering net. These two filtering nets are reused through updating and cleaning. Namely, a timer is installed within the air conditioner. After a predetermined time (for example 500 hour or 1000 hours) has elapsed, the air conditioner is stopped or a warning lamp is bright up for informing the user to update or cleaning the filtering net.
However, The prior art filtering nets of air conditioners are very rough, it can not decide whether the amount of collecting dusts has over a threshold value. Therefore, often, in a dirty environment, the filtering net is too dirty but still in use so that the lifetime of the air conditioner is reduced greatly. Inversely, in a cleaning environment, it is often a clean filtering net is updated due to preset time having been elapsed. These not only trouble the user, but also the cost of updating filtering net is increased.